1. Field of the Invention
The present invention relates to direct fuel injection in internal combustion engines generally and in particular relates to a system for more accurately determining when fuel injection should occur when there is a rapid acceleration that causes engine operation to change from a stratified fuel-injection operation to a homogeneous fuel-injection operation thereby causing the point of desired fuel injection onset to significantly advance.
2. Description of Related Art including information Disclosed Under 37 CFR 1.97 and 1.98
In each cylinder of a direct-injected internal combustion engine, the timing of the injection event relative to crank-angle position varies with engine speed and/or throttle position (load). It is desirable to operate direct-injected engines in a highly stratified mode during idle and low engine speeds and/or loads and to change over at some speed and/or load condition to running in a highly homogenous mode as set forth in commonly assigned copending patent application Ser. No. PCT/U.S. 97/10636 filed Jun. 20, 1997 and entitled "Improved Time Delay Ignition Circuit for an Internal Combustion Engine", which application is incorporated herein by reference in its entirety. In the current design of direct-injected engines, the spark timing remains relatively constant with the spark occurring at a selected crankshaft angle just prior to top-dead-center (TDC). When the engine is running in a stratified mode, the fuel-injection event is based on a well-known two-dimensional map or look-up table that plots speed and/or load versus crankshaft angle. As speed or load increases, the earlier the fuel injection occurs before top-dead-center. It is based on a variable crankshaft-angle position, and is defined herein as the "stratified mode" fuel-injection operation and the fuel injection occurs a short "time" (crankshaft angle) prior to the spark, i.e., the injection occurs in a crankshaft-angle range near top-dead-center. As speed and/or load increases, the injection event is gradually advanced further prior to top-dead-center based on this two-dimensional map or look-up table. At some selective crankshaft angle, upon attainment of a sufficiently high speed and/or load, it is well known that there is a changeover from this "stratified mode" fuel injection onset to the "homogeneous mode" fuel-injection operation. It includes a smaller variable range of crank-angle-based determination of the onset of the injection event. That range may include the 40.degree. immediately preceding bottom-dead-center and, again, a two-dimensional map, well known in the art, is used by the ECU to determine the exact crank angle position. At that point there is a significant instantaneous jump in the advance (movement further prior to top-dead-center) of the fuel-injection event. Thus the "homogeneous mode" of fuel injection is defined herein as engine operation after "changeover" occurs.
A frequent update of an engine operating condition such as speed and/or load condition is necessary to determine the proper fuel injection timing proper crankshaft angle) for each revolution. It is also desirable for optimal running quality that the update occur very closely (just prior) to the injection event so that the speed and/or load determination at the time of the update most closely approximates the actual speed and/or load at the time of the injection event. It would be apparent then that one would provide for such updates at some predetermined, regularly recurring crank angle. However, whereas this strategy is acceptable for conventional internal combustion engines in which the advance in the fuel injection is limited to some selective range of crank angles, in engines currently in production, where there can be a significant jump in the advancement of the crank angle at which fuel injection occurs, and in which the onset of the injection event may be at any crank angle, the single update position strategy fails. More specifically, utilizing a single constant update crank angle with such engines may result in the missing or skipping of an injection event when there is a changeover to the "homogeneous mode" fuel injection from the "stratified mode" determination of the onset of the fuel-injection event.